Neonchameleon
Legend
Actually, that's about what I'd expect during an adventure (20 good fights), but I agree the term is too vague to serve as a unit of measurement.
In BECMI and AD&D 1st Edition, you earned about two-thirds of your total experience from treasure, so taking that into account, a single adventure would have 6-7 good fights and leave the rest of experience to treasure finding. The thing is, you rolled treasure randomly on tables, and while sometimes you could get tons and suddenly advance just from opening a single chest, there was no expectation of finding such a significant amount that you could ever predict when you'd go up in level. In 2nd Edition, they changed the standard to no more experience from treasure, and if you played by that you'd really be advancing slowly and relying mostly on combats.
OK. So 20 good fights in BECMI was the actual practical number. I'd have said slightly fewer - but we're in the same ball park here. The 100 fights number is utterly irrelevant to practical play in the same way how long it would take me to walk to work is a figure that can be calculated but is irrelevant because I have never once walked to work. (I'd also have said 2-3 good fights and the rest easy other than attrition damage, but YMMV).
In 2e, XP changed. But you are doing exactly the same thing you did with BECMI and 1E - although this time it is possibly justifiable. XP for killing is the absolute minimum rate of advance, with optional rules including XP for GP, XP for Story, and XP for being a stereotypical member of your class (where for that 15 XP critter with the XP split between the party, the fighter got 10 personal bonus XP) whereas a first level specialist wizard has 100XP in their back pocket for casting useful spells per day and a Rogue gained 2XP per GP. The XP range is so variable in 2E that we can only rely on the ballpark suggestion "An average pace in an AD&D game campaign is considered to be three to six adventures per level" - and even that is a very loose statement, but I'd say that an adventure on average lasts about a session (and a module contains multiple adventures).
The treasure may also be hard to find by the way.
Of course it is. That's where player skill comes in.
In my personal experience, 10 gp went very far. 40 minutes to an hour could be spent role playing in a shop as you haggled with the merchant.
And in mine if you Greyhawked the place even a basic goblin carries about a GP worth of trade goods; a solid and reliable weapon like a mace or shortsword that you can sell to a merchant for about a GP. Some goblins carry bows - jackpot. (No one wants used goblin armour unless it's metal - chain is chain, but used goblin leather is horrible). Given that most of what mundane merchants sell is so cheap after about two adventures, 40 minutes to an hour haggling would be considered time wasted - which, I suspect, is party of why levelling up in most games was much much faster than you indicate. By mid second level if you stuck around your money would be no good at the local inn and petty cash was petty.